Comments

An “uncertainty” I have after reading Hansen’s storms book and also reading about the snowball earths, is where does Hansen’s pessimism about a Venus style runaway greenhouse come from? I read (can’t remember where) that CO2 reached atmospheric concentrations of ~10% in order to melt the snowball 600mya. Given that this did not lead to the oceans boiling why does Hansen say he believes that it’s a “dead certainty” if all tar sands etc are exploited? I know his view is not the consensus, but is the increase in solar output over the intervening 600my enough to make the difference? Or is it that there was something different about the post snowball world (e.g. weathering rates vastly increased by abundance of ice-ground rocks in post snowball period?)

The views of a few experts on this puzzle would be appreciated. Thanks.

It’s good to see that someone is looking to the future in the course of their jobs, and taking the climate scientists seriously.

I guess I should say someone *else* – the DoD and other groups have been looking at all sorts of climate instability for years.

I only read the summary of the document, but it’s also heartening to get the attitude of “clearly there could be a serious problem, and we need some help in better predicting just how much of a problem it will be *right here*”.

On a more pithy note, changing our climate and praying to the Divine for assistance is probably not a very healthy measure:)

I don’t think the sun has gotten that much stronger in 600 million years.

I also think you’re vastly over-simplifying things in your thinking. IE, I believe you posit that if we had 10% CO2 with the snowball earth 600 mya that 1000 ppm now couldn’t possibly drive us to the Venus syndrome.

During the snowball Earth event, volcanoes kept erupting under the ice, but weathering of rock to silicates didn’t happen because the newly exposed rock was a) under all the ice and b) cold. Temperature speeds up chemical reactions, and removing the ice exposed the rock to high levels of CO2. Eventually a combination of orbital changes and increased CO2 levels took us out of the snowball state and they did indeed lead to a “hothouse Earth”.

The Earth of 600 million years ago was a very different place; continental configuration was different, ocean circulation was different, plant and animal life totally different. You can’t just make a simple comparison between now and then. The sun was cooler too, but I can’t say how much.

What Hansen says in his book is that as little as 10-20 W/m^2 could drive us into the Venus syndrome with sufficient time, so the real question is how much we can do before crossing that threshold.

Indeed, methane still seems to me the BIG uncertainty–how much will be emitted how fast. In the last week, the Arctic melt has gone into hyperdrive–rates and levels never seen before.

On the general issue of uncertainty, denialists always point to any kind of uncertainty (of which there is always some) as a sign that there is nothing much to worry about, since it might be much less harmful than predicted. But of course the uncertainty cuts both ways, and, IIRC, the fat side of the tail is on the not-so-benign side of things.

Also, there are two kind of uncertainty–uncertainty about future global average temps and uncertainty about effects in particular locations. Obviously the latter uncertainties are much higher, but people actually live in particular localities, so the certainty they most want is the certainty modelers are least able to give.

Any comparison of Earth to Venus is disingenuous…Venus’ atmosphere is made up of 97% CO2 while Earth’s is 36/100ths of 1%. Apples and oranges people.

[Response: not really. Venus is good example of a) a demonstration that very high amounts of co2 lead to very high greenhouse effects, and b) what happens when all the water evaporates, which will happen to the Earth in a few billion years. On a more technical level, the atmospheric physics on Venus has a lot of analogies with aerosol, chemistry, and cloud processes on Earth. – gavin]

Gavin: <…what happens when all the water evaporates, which will happen to the Earth in a few billion years.

Uh-oh. I hear a new argument: “Nature will evaporate all the water on Earth in a few billion years, humankind’s contribution to global warming is insignificant, and by the way I have a lot of coal to sell you.”

With regard to the uncertainty prayer, the older I grow the more often I find myself answering questions with “It depends.”

I enjoyed the prayer almost as much as I enjoyed Schmidt and Wolfe’s definition of a greenhouse gas in Climate Change: Picturing the Science. I had always thought that acceptance should come before serenity in the original version, and this seems to circumvent that nerdy quibble while having a good scientific spin to it.

As for the discussion that has quickly evolved…The question of at what threshold does the Earth succumb to the runaway greenhouse is fundamentally a question of at what point does the greenhouse effect of water vapor (and the corresponding increase in the saturation vapor pressure by increasing temperature) wins the race against condensation. The history of runaway greenhouse studies has shown that individual infrared-active substances have associated with it a critical point that depends on the solar flux, and whether a planet is above or below that threshold determines whether the water (or whatever else) primarily exists as a liquid ocean or as vapor in the atmosphere. Ingersoll (1969) was one of the first to clearly point out that the outgoing radiation flux has a maximum value when water vapor becomes a significant constituent in the atmosphere (the argument doesn’t need to apply specifically to water vapor, but it is most common). If the incoming solar flux exceeds the limiting outgoing radiation term, then the planet must continue to warm up because it has no way of getting rid of the imbalance and the oceans boil away. When the oceans are evaporated and the atmospheric mass becomes fixed again, the OLR becomes free to increase again (particularly if temperatures are hot enough for the planet to radiate significantly in the visible and near-infrared where water vapor opacity is relatively low).

The question of at what limit the OLR vs. T curve flattens out depends also on the acceleration due to gravity, but uncertainty in clouds preclude confident estimations of where this threshold actually exists. However, it does not appear to lie much lower than about 1.4 times the current solar constant (see Kasting, 1988) and so even if one were to lower the albedo quite a bit, it seems we would be quite safe from the prospect of a runaway greenhouse. Note that the limiting OLR (also known as the Kombayashi-Ingersoll limit) is only weakly dependent on the CO2 concentration. CO2 has only a minor effect on temperature anyway once water vapor becomes a dominant constituent in the atmosphere, and actually, it’s possible to get a wet stratosphere and lose lots of water vapor to space through photodissociation even prior to the full runaway. Thus, even if we did burn all the coal today, there is no physical way that we could really kick in a runaway greenhouse (unless, I suppose, clouds did something really weird to dramatically accelerate the warming).

By the way, just as a matter of clarification for the comments so far: The evolution of solar luminosity with time can be roughly fit by the equation (Gough 1981):

L(t)=L_o*[1+(2/5)-(2t/5t_o)]^-1

where L(t) is the luminosity at time t, and L_o is the modern luminosity at the current age of the sun, t_o . If the ratio of t/t_o is about 0.87, as it would have been in the neoprotezoic, then it follows that the luminosity would have been 95% of today’s value. The luminosity is directly related to the solar insolation at Earth by a constant if the distance to the sun does not change, and so the solar constant at the neoprotezoic would have been 0.95*1370 W/m2 = 1300 W/m2. As I’ve stated before though, the Earth is comfortably below any incoming radiation threshold in the present to get a runaway greenhouse, regardless of what happens with CO2. It will take some billion years or so of star evolution to kick in a runaway.

We could perhaps add “the wisdom to know what these uncertainties mean in practical terms.” But that gets us to (or beyond) the frontiers of science and politics, doesn’t it? Wili’s comment (#6) is particularly apposite in that regard.

Decomrf, I’m not expert, but as I recall, Hansen’s worst case scenario is a triple-whammy of 1) a stellar luminosity increase (he cites the 2% increase in luminosity since 250 million years ago as equal to a doubling of CO2), 2) uncertainty in CO2 proxies from 250 million years ago (2000 ppm was safe then under the dimmer sun, give or take 1000ppm), and 3) saturation of natural carbon sinks foiling the Earth’s capacity to absorb emissions.

Added to these, he descibed methane hydrates as having built up since their last big release 55 million years ago, and being primed for another release should ocean currents warm and or change their paths. He also suggested that there is a possibility that ocean currents reorganized 55 mya with deepwater forming in the Pacific. Such an event today could warm vast stores of methane hydrates.

I would add that if I accept his argument that uncertainty in proxies from 250 million years ago doesn’t provide a safe limit, then guesses about snowball earth conditions farther back are also suspect.

dcomerf: Roughly speaking the sun has been increasing its output by about 1% every 100 my. That means that it is about 5% to 10% hotter now than it was 600 mya. That is really quite a lot. What’s keeping the Earth from being very warm is the relatively low concentration of CO2 in the last million years or so.

We really don’t need high CO2 concentrations to go along with a warmer sun.

How can you work with uncertainties you can’t reduce? Sounds like Donald Rumsfeld talking to me.

Michael

[Response: People do it all the time. It’s uncertain whether your house will burn down. You buy insurance. It’s uncertain whether it will rain next weekend. You pack an umbrella. etc. Indeed, if you think about it, very few of the decisions you make about dealing with future events are made because it is certain what will happen. – gavin]

From Chris Colose 11, I take it that to the best of our knowledge run away green house cannot be triggered currently by burning fossil fuels. From JG 13, I understand that Hansen argues that the best of our knowledge is uncertain, and if we are in error in the wrong way, run away greenhouse could be triggered by burning fossil fuels. This leads me to two questions.

First, does Chris Colose (or the consensus of opinion) agree with Hansen that our knowledge is still that uncertain?

Second, presumably if our error in estimates paleo CO2 concentrations where in error in the opposite direction to which Hansen allows, then the sceptics would be right (or nearly so) in their conclusions if not their methods. So what is the relative probability of an error sufficient that runaway greenhouse is a real possibility, compared to probability of an error sufficient that business as usual will result in greenhouse warming of less than 2 degrees C? In essence, who is wackier – a “warmist” who thinks that runaway greenhouse is probable in the next few centuries with business as usual, or a sceptic who thinks we need to nothing to avoid significant adverse impacts from greenhouse gass emissions?

BTW, there’s a confusion in terminology that crops up once in a while: in this thread, “runaway greenhouse effect” has been taken to mean “running away to extremely high temperatures,” such that, as Chris writes, the oceans basically evaporate.

However, you also see this phrase used to describe a scenario in which natural feedbacks come to dominate the warming process such that mitigation of human GHG emissions becomes essentially insignificant–that is, the greenhouse effect becomes a “runaway” from (potential) human control. I can’t recall for sure if he used the phrase or not, but this scenario is envisioned in Gwyn Dyer’s Climate Wars.

I love it, great words, great thoughts, and very true. This is what guides me polar cities work, which nobody wants to discuss in public for fear of having their PHDs and careers ruined. SIGH. But polar cities are coming, in fact, as one brave PHD told me, they are already here. Think about what he meant!

Kevin McKinney, the thing about the distinction you draw in comment currently #17, is that once the second meaning of “runaway greenhouse effect” is realized — and “feedbacks come to dominate the warming process such that mitigation of human GHG emissions becomes essentially insignificant” — there is no way at present to be confident that the result will not be realization of the first meaning.

Re 11 Chris Colose – Very nice post. An important point: it isn’t actually necessary to reach a runaway water vapor feedback and sustain it for the oceans to be removed (and leave CO2 with no geologic sink*?*); maintaining some lesser warmth can over time allow ocean removal by increased stratospheric H2O leading to enhanced H escape to space. Of course, regarding AGW, is there any way that CO2 and feedbacks could sustain such warmth for long enough to destroy the geologic CO2 sink*?* before the geologic CO2 sink prevents that fate – I’d guess no at this point, though I haven’t gone through those calculations.

** – more rapid (globally) inorganic geologic CO2 sequestration is favored by a coexistance of warmer wetter conditions (with more CO2) with sediment/debris containing silicate minerals with certain ions. However, the process can switch from reactant-favored to product-favored at sufficiently high temperatures (depending on the cations/minerals involved and the partial pressure of CO2) – which of course is why there are inorganic geologic CO2 emissions.

Of course, geologic organic C burial requires photosynthesis with incomplete oxidation – can happen to some of the organic C sinking within the oceans, on relatively flat land regions depending on climate.

PS how much would the methane residence time in the atmosphere increase as atmospheric methane is increased?

PS much much much much less than a Venus-like scenario is plenty enough justification to reduce CO2,etc emissions.

… But about ocean removal – it isn’t just the mass of water in the oceans (and groundwater, surface water, ice, vapor and clouds) – there is also water in the mantle which may tend to replenish the ocean if water is removed by H escape (James Kasting did a paper on a (proposed?) mechanism that may act as a negative feedback to changes in ocean depth over geologic time). Not an infinite well, though.

Let me put a different twist on the “Uncertainty Prayer.” The problem is that it is simplistic in seemingly assuming that we can identify all the important uncertainties. So, my twist:

Grant us…

Ability to reduce uncertainties that science identifies;
Willingness to work with those we cannot reduce;
Wisdom to anticipate unknowns that we can’t possibly imagine;
Awareness to leave an ample margin of safety for all of them; and
The Strength to do so very fast.

We are engineering the structure of our climate incrementally both through our daily global actions and the diplomatic and legislative steps of policy making. No professional engineer would design a structure without an ample factor of safety. This is not just about the science, it is about how to apply the science we have now as well as the science we have yet to gain, safely. If we don’t do both, we can expect to fail.

This is especially critical regarding climate, where to be successful our mitigative actions must be taken years or decades in advance of clear indicators. When we have the clear indicators, it’s too late for action then.

What this entails is – as a society – distinguishing between wants and needs, and then reevaluating some of our needs. Especially so with our population projected to climb to 9 billion over foreseeable decades, which is both a problem that must suppress wants and is one of said “needs.”

Gavin, it looks like the appeal to God has been made more, er, implicit this time than is usually the case in climate change discussions. This is progress! I’d say that all we need now is a “Dear Lord” at the beginning and we’re done. ;-) Best, Alex

There is always uncertainty in scientific thought so the third point is what really matters. Every now and again there is a paradigm shift in knowledge when issues that were uncertain become clear. Was it Debye (or Hildebrand) who said that if something was not yet simple it was not yet right? So we persevere – and wait for those paradigm shifts!!

“Response: People do it all the time. It’s uncertain whether your house will burn down. You buy insurance. It’s uncertain whether it will rain next weekend. You pack an umbrella. etc. Indeed, if you think about it, very few of the decisions you make about dealing with future events are made because it is certain what will happen. – gavin”

You do not remodel economies and civilisations based on uncertainties. There is a big difference between an umbrella and a whole economy.

[Response: Perhaps you are being deliberately obtuse – but you will find that many economic decisions are made in spite of uncertainties. Do all investments work out? No. Yet people continue to invest. Did the TARP program guarantee the future functioning of the financial system? No. But it was tried anyway. Did the stimulus packages provide for certain economic recovery? No. etc… – gavin]

“I love it, great words, great thoughts, and very true. This is what guides me polar cities work, which nobody wants to discuss in public for fear of having their PHDs and careers ruined. SIGH. But polar cities are coming, in fact, as one brave PHD told me, they are already here. Think about what he meant!

Let’s say you’re thinking about some action to take in the future. You have two possibilities: you can do A or you can do B. You also have uncertainty about the costs and benefits of each action.

One way of making that decision is to weigh the various costs and benefits in light of their respective uncertainties, and come up with a best guess about whether A or B would most likely lead to a better outcome. That’s the approach we’d use in almost all circumstances.

Another approach would be to say “There’s a lot of uncertainty, so no one really knows which would be better. Therefore, I’ll do A.” That’s essentially Steckis’s approach.

Somehow, the existence of uncertainty becomes a justification for not making any changes to our economy and infrastructure, but it isn’t a justification for not adding hundreds of gigatons of CO2 to the atmosphere.

31 Richard Steckis: “And not a single low or mid or high latitude city has been abandoned in the last century or so due to climate.”

And we all know what happened in an area of the world which ignored the warnings of a meteorologist, even threatened him with physical violence, who had discovered (through examining the historical record) thatthe area could be hit by a large tsunami any time soon: Boxing Day 2004.http://riskman.typepad.com/perilocity/2005/01/tsunami_smith.html

“You’d really have to go digging into very old historical records and the scientific literature and extrapolate from what’s there to find that yes, there could be effects (leading to tsunamis) in Thailand,” says Phil Cummins, a seismologist who studies the region at Australia’s national geological agency. “But he was correct.”

jg (#13),
Thank you for your graphical summary but it doesn’t tell me how a runaway H2O greenhouse is supposed to happen in the first place. As I understand it, the scientific consensus has long been that a few thousand ppm of CO2 would not materially affect the theoretical Kombayashi-Ingersoll limit which depends on the gravity of the planet and tells us how much non-reflected solar radiation is necessary to make a runaway greenhouse possible for a particular molecule. And we’re not supposed to be close to the limit. I suppose that an unknown cloud regime might possibly make the limit irrelevant… is that what Hansen’s arguing? Or is he arguing that the reasoning behind the limit is bunk? Or something else entierly?
To put it in the terms of Gavin’s prayer, it’s not rational to be willing to work with ANY risk of such a runaway. It’s effectively an unacceptable, uninsurable infinite risk. You simply don’t go there. Life on Earth isn’t a limited liability corporation. ANY chance higher than zero of a runaway happening would be much worse than, say, a 99% chance of 6C global warming and would justify ANY means of stopping this trainwreck. All these consensual climate summits would go out of the window for one thing because thermonuclear weapons would come into play. These are the tools which have been designed to deal with existential threats.
I’ve been led to believe the risk is zero. But Hansen has been saying it isn’t zero for a while… and it’s past time for his colleagues to tell us in no uncertain terms if he’s making any sense.

Tom Curtis,
Uncertainties on CO2 sensitivity are asymmetric. Our confidence that CO2 sensitivity is not below 2 degrees per doubling is equal to that of it not being above 4.5 degrees per doubling. However, we are still in trouble if it is 2 and in deep kimchee if it is 4.5. Uncertainty is not the friend of the complacent here.

30, Richard Steckis: You do not remodel economies and civilisations based on uncertainties.

that’s an odd comment. Economies and civilizations are continuously reinvented based on entrepreneurs’ (and other’s) assessments of calculated risks and benefits, all of which have always been uncertain. Right now, China (among others) is refashioning its economy and civilization by expanding renewable energy supplies based on the uncertain calculation that fossil fuel-based energy production is unsustainable — it leads the world in biofuels-related patents. Back when no one could imagine a Boeing 747, or even a P-51 Mustang, inventors and entrepreneurs started building the aircraft and airline industries.

Whenever there are uncertainties, going forward to determine a course of action, most scientists develop pilot projects; usually a series of pilot projects to answer a number of questions. In error, a less well experience researcher attaches importance to a pilot project yielding looked for results. This fixation upon “preliminary results” most times leads scientific inquiry “down the garden path.” Not seen nor accounted for, as dictated by uncertainties, are the pilot projects that answer other questions. There seems to be this rush to winow away all conflicting information from what appears to be a winning idea. The history of science is littered with such “golden boy” projects, when we have not listened to critics who say: “not so fast.”

1. Admit we are powerless over global warming — that our climate has become unmanageable.
2. Come to believe that climate scientists more knowledgeable than ourselves can restore us to sanity.
3. Make a decision to turn our will and our lives over to the care of climate scientists as we understand them.
4. Make a searching and fearless inventory of our climate change skepticism.
5. Admit to God, to ourselves, to another human being the exact nature of our climate change skepticism.
6. Be entirely willing to have climate scientists remove all these defects of character.
7. Humbly ask climate scientists to remove our shortcomings.
8. Make a list of all the climate scientists we have harmed, and become willing to make amends to them all.
9. Make direct amends to such people, wherever possible, except when to do so would injure them or others.
10. Continue to take personal inventory and when we were wrong promptly admit it.
11. Seek through prayer, meditation, and research to improve our knowledge of and conscious contact with climate scientists, as we we understand them, praying only for knowledge of their will for us and the power to carry that out.
12. Having had a scientific awakening as a result of these Steps, try to carry this message to other climate change skeptics, and practice their principles in all affairs.

where you can read, among much else
“… a value known as the Kombayashi–Ingersoll limit. This is the limit to how fast a planet with a moist atmosphere can lose energy by infrared radiation…. The precise value one obtains for the limit depends on the treatment of infrared absorption properties of water vapour at high temperature and pressure…. we have sketched in the value from ref. 42 (about 320 W m–2), and the reader is referred there for further details.”

Comment by Mike Cloghessy — 29 June 2010 @ 5:16 PM
Any comparison of Earth to Venus is disingenuous…Venus’ atmosphere is made up of 97% CO2 while Earth’s is 36/100ths of 1%. Apples and oranges people.

[Response: not really. Venus is good example of a) a demonstration that very high amounts of co2 lead to very high greenhouse effects, and b) what happens when all the water evaporates, which will happen to the Earth in a few billion years. On a more technical level, the atmospheric physics on Venus has a lot of analogies with aerosol, chemistry, and cloud processes on Earth. – gavin]

Forgive me Gavin but in your response you forgot to mention Mars which has a high Co2 content (though further away). Let’s look at it another way, what if Earth had the same atmospheric composition as Mars then would Earth be warmer or cooler than it is now. I also think that atmospheric pressure on Venus has a part to play here but what do I know. Yeah I know – “nothing”

[Response: Not sure what your problem is, but there is a greenhouse effect on mars exactly as would be predicted. There is more co2 sure, but the pressure is less and so line absorbances are less and there are no other greenhouse substances. -gavin]

30, Richard Steckis: “You do not remodel economies and civilisations based on uncertainties.”

I have to agree with Septic Matthew: that is an odd comment. Richard, can you point to a single economy or civilization that has been established on the basis of complete certainty?

I suspect the reason some people have difficulties with regard to understanding certainties (and I’m not directing this to you, Richard) is that they don’t quite realize how their lives are ceaselessly embroiled in uncertainties, moment to moment, day by day, year by year.

I have another poem (well a prayer really) in response, relating to managing expectations of what we can expect government will achieve when tackling climater change. I think it is secretly said by governments all over the world.

The Official Government Prayer

Our government, somehow elected
Delusion be our game.
My god we’re dumb
But there’s work to be done
And blame to be deflected.
Delay us today our daily decisions.
And forgive us our empty promises,
As we forgive those who make empty
promises in response.
And lead us not into innovation,
But deliver us from progress.
For we have the politicians,
With the power, and the will
To speak drivel
For ever and ever.
Amen.

I read Hansen’s “Storms of My Grandchildren”. It was interesting, and I understood that Hansen sincerely wants to mitigate climate change, but I felt that Hansen did not explain uncerainty of his outlook enough. I felt so partly because I had just read Stephen Schneider’s “Science as a Contact Sport”. I expected the expressions of uncertainty (likelihood, confidence etc.) which Schneider had promoted to be used by IPCC. I do not think Hansen needed to follow that scheme in his book. But I felt that he should mention the magnitude of uncertainty more explicitly anyway. I understand that he points to the worst end of the probable range of his outlook, when he tell runaway greenhouse effect, or rapid complete melting of the Greenland ice sheet, out of precautionary principle. But I guess that a non-expert reader is likely to understand that Hansen tells the most probable outlook.

I also read Gwyn Dyer’s “Climate Wars” (mentioned by Kevin McKinney (#20)), and William Calvin’s “Global Fever”. Their outlooks of climate change seemed to me similar to Hansen’s.

Hansen (in popular writings, not in peer-reviewed scientific articles), Dyer and Calvin commonly emphasize the possibility of runaway situation as mentioned by Kevin McKinney: climate change will be dominated by reinforcing feedbacks and human intervention cannot stop it. In other words, the climate system will go beyond a tipping point.

Even though IPCC has discussed such possibility (in Box 10.1 of AR4 WG1), the main storyline of the IPCC reports is not that one. Though the climate system is not linear and full of feedbacks, the response of global mean temperature to CO2 concentration is bounded in a certain range, and it will be able to respond to reduction of emission with a considerable delay.

Recently I saw a so-called climate skeptic writing something like “IPCC promotes CAGW theory”. It took some time until I decifered CAGW as “catastrophic anthropogenic global warming”. It seems that the person thinks that majority of climate scientists tell such stories as in Hansen’s book as probable scenarios. If so, it is natural for him to consider that majority of climate scientists overhype global warming. Very unfortunate misunderstanding.

We need precautioners who point to the worst end of the probable range. We also need another group of scientists who show the whole probable range of projections. We should make clear the distinction of the two groups.

It just occurred to me that the axial tilt of earth -23 deg- and the associated seasons may provide a strong negative feedback to greenhouse runaway. Even if temperatures rose enough to start lowering sea level by evaporation, it would still rain at the pole during winter. The lateral transport of heat from the tropics would bring copious quantities of water vapor and latent heat; release of the latent heat requires condensation -> precipitation. Cold falling precipitation doesn’t warm by compression, and provides a powerful mechanism to remove heat from the lower atmosphere. It would have to be very hot at the beginning of winter for the Arctic basin to stay above temperatures required to prevent the eventual collection of liquid water during six months of winter. What would the surface pressure and temperature have to be to maintain the top km of the ocean as vapor?

I wonder if increased precipitation in fall & early winter of 2009 transported latent heat into the Arctic, leading to the delayed peak of ice extent compared to previous years, as well as decreasing surface salinity and contributing to the higher peak extent seen this year? Steven Goddard had his knickers in a knot over at WUWT a while back over the heavy & early snowfall in North America – did that extend to the Arctic? (He hadn’t noticed that the decline in spring & summer snow cover was much larger; when I pointed this out, his response was “I’m guessing that you aren’t located in Washington D.C.”

The long tail to the right of this implies skewness risk..These are low probability but hight impact scenarios that a risk averse agent would like to avoid..In other words, the skewness of this distribution is/should be an incentive to take action on climate change..

Why this preoccupation with uncertainty? Even this prayer stress uncertainty. What is wrong with you natural scientists :-P
Uncertainty is not that relevant for solving the climate problem and that reducing uncertainty is the goal of science is a very limited view of science. More so the belief that reduced uncertainty will help policymaking.

Andreas,
Actually, the uncertainties are critically relevant. At present the risk calculus is dominated by the high end of the probability distribution for climate sensitivity. If climate sensitivity is in the range of 2.1 degrees per doubling (bottom end of the 90% confidence interval), we still need to act, but probably have sometime to phase in action. If it is at the favored level of 3 degrees per doubling, immediate action is crucial. And at the upper end of the 90% CL of 4.5 degrees per doubling, the appropriate action would be to SLAM ON THE BRAKES NOW.

And because the consequences of climate change rise so dramatically with temperauture increase, it’s really the portion above the 90% CL (with probability~5%) that dominates the risk calculus. And this is just looking at the known risk–not taking into account tipping points such as loss of polar ice or outgassing of melting permafrost or clathrates.

In probabilistic risk assessment, it is the uncertainties that wind up driving risk. If those uncertainties prevent us from bounding risk at all, risk avoidance becomes the only viable strategy.

Ray, your response is exactly like I expected from a member of the natural scientists that I critiqued. Yes, uncertaintly are critically relevant for YOU, given the limited ways that you look at the world trough your disciplinary lenses. However, neither scientists, nor politicians or the public are that hyper-rational, and other scientific disciplines stress other uncertainties or dont care at all about that. We will in a world full of uncertainty and we make holistic evaluation on what to do and avoid. The natural science types of uncertainties are just a smaller part of the things that counts, also when it comes to handling climate change.

I’d like to second Josh’s plea (at #51) for a thread on what is happening in the Arctic. The season is already breaking all sorts of records. Graphs of ice volume are going through the floor. The sea ice anomaly graph is dropping more dramatically than anything seen since it started in 1979. The ice coverage maps are exploding with the bright colors that indicate melt, all across the Arctic.

We need some professional perspectives on these events, events that seem to us ominous in the extreme.

I know relatively unpredictable things like wind patterns and cloud cover can change thing quickly, but it would be nice to hear if anyone had predicted this rate of melt, and what their predictions were based on, if nothing else than for scientific interest and input for future modeling.

Andreas, yes people make off-the-cuff decisions about risk, and repeatedly, these decisions have been shown to be flat-assed wrong. Our species sucks at risk assessment. We over-emphasize spectacular risks like terrorism an under-emphasize risks in 1)activities we cannot or do not want to avoid (like driving eating at McDonalds or sex) or that are remote in time (e.g climate change or smoking related illness). That is why it is imperative that risk be approached in a systematic manner with proven efficacy, like probabilistic risk assessment.

By the way, you will get the same answer not just from natural scientists, but from any discipline that deals with risk, viz. Harmen’s insightful comment #67. Good lord, man, you sound like a teenager who thinks he’s the first ever to fall in love!

Thanks, Kooiti, for a great expansion of the idea I briefly put forth, as well as the titles–particularly the Schneider and Calvin books, which sound as if they should go onto my reading list.

I agree, FWIW, that clarity around “worst case” versus “most probable case” is much to be desired. I’d suggest that Dyer’s willingness to look at worst cases comes partly from his military background–military planners, I’m told, spend a lot of thought on worst cases, and indeed the worst case was traditionally the one you were supposed to plan for as your primary contingency, I believe. Then focus shifted a bit to emphasize the most likely scenario more–IIRC. A lot of Dyer’s best stuff comes from his interviews with military planners.

Any comparison of Earth to Venus is disingenuous…Venus’ atmosphere is made up of 97% CO2 while Earth’s is 36/100ths of 1%. Apples and oranges people.

[Response: not really. Venus is good example of a) a demonstration that very high amounts of co2 lead to very high greenhouse effects, and b) what happens when all the water evaporates, which will happen to the Earth in a few billion years. On a more technical level, the atmospheric physics on Venus has a lot of analogies with aerosol, chemistry, and cloud processes on Earth. – gavin]

You could add that Venus and Earth’s atmosphere can both be successfully modeled using the same framework – a radiative-convective balance model that relies on quantum physics and fluid dynamics theory. What this means is that we generally understand how planetary atmospheres operate on a very large scale, as long as we are given variables like pressure and chemical composition.

On Venus, the chemical composition is a result of active volcanism. On Earth, this also plays a role, but biological activity over several billion years is a more important factor. Mars looks something like a fossil planet – a low pressure atmosphere, in chemical equilibrium, mostly CO2 – but the same radiative-convective approach works there too. Understanding the composition in more detail requires developing biochemical and geochemical models for “earth system processes” as they’re called.

Since this thread is supposed to be about water resources for managers, the runoff models they describe in the paper are of interest – they take climate variables from global climate models and use them as external input for local watershed and river flow models.

Physically based models try to simulate key physical processes of a system. In the case of runoff, they try to account for the fate and transport of water molecules in the system. For example, does the precipitation fall as rain or snow? If it falls as snow, does it stay in the snow pack, when does it melt, and does it ablate? If it falls as rain, does it run off the surface, or percolate below the surface? If it goes below the surface, does it go into an aquifer, does it go into a stream, or is it absorbed by vegetation? These processes modeled are based on what is known about physical and biological processes.

The regional trends here are going to vary – but the American west is looking at earlier spring runoff, perhaps greater variability in winter precipitation, and late summer droughts associated with severe wildfire seasons in the summer and fall. Even though the warming trend is steady, the greatest source of year-to-year climate variation will continue to be ENSO. Extreme events of interest include summer heat waves and warm spring storms that release massive floods due to melting snow.

Incidentally, there is absolutely no evidence for any kind of “Pacific cooling cycle” to counteract the general warming trend, despite the promotion of this theme by politicians like Barton and Inhofe, and scientists like Easterbrook. In fact, when it comes to the PDO, people can’t seem to agree if we’re in a ‘cool phase’ or a ‘warm phase’, or even what the clear indications would be, or how the signal for this putative cycle can be extracted from the ENSO system, the warming trend, and the variability introduced by volcanic explosions…

Ray writes “By the way, you will get the same answer not just from natural scientists, but from any discipline that deals with risk”

That is not true. Your answer is typical of natural sciences based on applied mathematics, as most natural science are, with a positivistic view on science, as most natural sciences have.

If you read Ulrich Beck, probably the most famous sociologist dealing with risks, e.g. the book Risk society, you will experience a very different approach to risk.

But the point with my first critique (which I didnt state explicitly) was to critique the linear model of science and policymaking, which the IPCC are based upon as well as most atmospheric related sciences. The linear model assume that reduced scientific uncertainty is required to reach a political concensus. This assumption has been falsified thousands of times in emprirical studies in the social science, still most natural sciences believe the linear model to be true. You guys focus on uncertainty far too much, and in doing that you gridlock and f**c up the climate problem …

[Response: Why is it that you keep setting up this strawman? No-one that is discussing these issues at the modelling centers or at the IPCC are following this caricature of what you think we think about the science/policy interface. Just get over it. – gavin]

Andreas,
Who said anything about political consensus–or politics for that matter. I am talking about estimating and bounding risks so that the policy makers have a quantitative guide for allocating resources.

Allowing resources to be assigned based solely on public outcry or political influence or “hunches” doesn’t work–demonstrably. If you look at how risk professionals allocate resources, it is based on probabilistic risk assessment. Learn it.

Gavin, what kind of expertise, studies and methods are you relying on when you state that? None I guess, or?

[Response: I hardly think I need a published study to know what I think, what i am discussing or what interactions I and my colleagues have with policymakers. -gavin]

I can give you many referenses to prominent social scientists that studied the science/policy interface of climate change. Most, it not all of them, agree with my statement.

[Response: Well that obviously trumps actual experience. -gavin]

For example, to build a scientific concensus and that a political concensus would follow sooner or later was a firm belief of Bert Bolin, first chairman of the IPCC. He argued that reducing uncertainty was the means, and that one had to do that carefully becauce exaggerations runs the risk to backfire (e.g. sceptic attacks on too scary scenarios that cant be backed up with facts), and in that way, in 10, or 20 years time, the IPCC would have been instrumental in establishing a political concensus, which was the utlimate goal of Bolin as the chairman of the IPCC. Why cant we be honest about such things? Is honesty really that dangerous?

[Response: Lovely, disagreeing with your characterisations means I’m not being honest. You do really have a way of charming the scientists you purport to study. But think about this, is it conceivable that attitudes and thinking have changed over 20 years? Is it possible in fact that scientists have actually absorbed some of that research you pride so highly? Now, if you were honest you’d at least consider the possibility…. -gavin]

It certainly is my work…although I suppose I should acknowledge the Lord’s Prayer for the general form. It passed the time one day when I was very frustrated with my political masters (this a normal state of mind for me) and then sparked off a whole satirical manual.

The procedures are there for a reason. If you are not following them, you aren’t approaching the problem properly, AND you could be breaking the law in some fields. Political consensus is another beast entirely. That will come when people decide they actually care whether their progeny live or die…or not.

Comment by Jimbo — 30 June 2010 @ 7:21 PM
Forgive me Gavin but in your response you forgot to mention Mars which has a high Co2 content (though further away). Let’s look at it another way, what if Earth had the same atmospheric composition as Mars then would Earth be warmer or cooler than it is now. I also think that atmospheric pressure on Venus has a part to play here but what do I know. Yeah I know – “nothing”

[Response: Not sure what your problem is, but there is a greenhouse effect on mars exactly as would be predicted. There is more co2 sure, but the pressure is less and so line absorbances are less and there are no other greenhouse substances. -gavin]
—–
JIMBO RESPONSE: Thanks for the update. You really should have known better when responding to Comment by Mike Cloghessy — (29 June 2010 @ 5:16 PM) and mentioned pressure, otherwise some people would have simply accepted your very simple initial response to Mike as cut and dried.

Jimbo at 91 said:”JIMBO RESPONSE: Thanks for the update. You really should have known better when responding to Comment by Mike Cloghessy — (29 June 2010 @ 5:16 PM) and mentioned pressure, otherwise some people would have simply accepted your very simple initial response to Mike as cut and dried.”

You were the one who mentioned pressure, not Mike or Gavin in his response to Mike.

The page you linked does not say “people can’t seem to agree if we’re in a ‘cool phase’ or a ‘warm phase’” as you labelled, but “It appears that we are still in the cool phase of the PDO”. The cool phase here is the broadly La-Nina-like phase.

Maybe some other people call the same phase as “warm phase”, by looking at temperature at a different part of the Pacific ocean as indicators. If so, it just means that the terminology has not been settled.

PDO does not have a regular periodicity (as is ENSO), and is difficult to predict. It will certainly be source of noise to the prediction of global warming. But a recent study shows some predictability of PDO for several years when good observations of the initial condition in the ocean is available. See the paper:
T. Mochizuki et al. (2010): Pacific decadal oscillation hindcasts relevant to near-term climate prediction. Proc. Nat’l. Acad. Sci., 107, 1833 – 1837. http://www.pnas.org/content/107/5/1833

Gavin, yes I actually do think that systematic studies of many individuals and cases that apply the scientific method are better than introspection based on more or less one individual *

[Response: My statement was concerning what I and my colleagues think and do. You apparently feel that studies about scientists 20 years ago provides more enlightenment about what I think, than me telling you. Bizarre. – gavin]

Yes, it is conceivable, even likely, that attitudes and thinking have changed over 20 years? Unfortunately, the linear model seems to still be the dominant attitude among scientists. For example, I studied a swedish case from 2008, and the linear model is still very visible.

[Response: I’m not saying that some scientists might still think that all they have to do is put the science out there and policies will just appear, but this is not what I think and it is not the paradigm in which most of the conversations I have with colleagues and policymakers takes place. I would have thought you would be happy about this, but instead you insist I must be wrong and that you are still free to characterise us as naive savants. Stop trying to feel superior to scientists and actually talk to them. Who knows, you might learn something. – gavin]

* Compare with this example:
IPCC: Climate is changing, 100 studies concludes, and the results are statistically significant.
Introspecto: This summer feels hot, I remember that the summers of my childhood was hot.
Who would you invest trust in? According to your reply to me, you prefer personal firsthand experience, so guess you go for introspecto ….

[Response: Don’t be silly. We aren’t talking about whether a single person’s opinion about the real world is more reliable than a well-done assessment, but about whether a single person statement about their opinion is more reliable than a report about a bunch of other scientists opinions. – gavin]

Most everyone here would put their trust in an experienced practicing scientist, as opposed to a young turk still trying to justify the money wasted on his education in pseudo-science. You are the “Introspecto” here.

Gavin,
You twist my words, and change yours, in order to win the debate. I know I do the same sometimes. That´s one reason why debates are frustrating, the goal are usually to win (scientists have big egos), and the means includes various “tricks”. For example:

I started out addressing natural scientists in general, especially the hard sciences, and so did you when you included the IPCC and more. But you end up to narrow it down to yourself (and some collegues). This is a smart “trick” because it changes everything to your favor (introspection is not a bad method to study oneself and you may not be representative …).

But I´m not that interested in you, more so in natural scientists in climate change in general. We can discuss you, sure, but than we have to begin from the start¨. I´m not a gavin expert, but I have noticed your superior attitude ;-)

– You persist in claiming that my empirical basis is twenty years old, and that things have change since than, although most studies that I rely on are from the last 10 years, my study are 2 years old, and these studies don´t really find any great changes. The changes are more rhetorical in parts of the social science that embrace stakeholder models, but the science/policy interface are still designed according to the linear model, and that is especially true of the IPCC, and no changes in that direction are visible in the outline of AR5, the procedures, etc. IPCC cling to the view of science as objective uncertainty reducer and that this mission is highly relevant for politics and policy at the same time that the IPCC is fully unpartial, disinterested and so on.

[Response: This has nothing to do with ego, and everything to do with the way you make repeated and vague generalizations about ‘scientists’ when commenting on issues that are very specific to me and my colleagues. You started off implying that the statement on uncertainty posted above was clear evidence of the linear model in practice. Since I posted that statement, you are clearly implying that I was following the ‘linear model’ and since I don’t think I do, I suggested that you stop setting up strawman arguments (something I still suggest you do). I do not consider the IPCC to be the sole connection between scientists and policymakers on climate-related issues, and (as we have discussed many times) neither is it the hot-bed of political activists you imagine it to be. There is an interesting discussion to be had about the complexities of this interface, but that discussion can’t even start while you insist on assuming that every scientist you talk to is naive and hopelessly ignorant about policy issues. Stop tossing around cliches about the IPCC ‘clinging to its role as an objective uncertainty reducer’ and actually ask people how IPCC deals with uncertainties – whether they are reduced or not. Ask people what other interactions they have with policy makers outside the IPCC framework, etc. etc. I have absolutely no objection to people looking at the science-policy interface as an academic study, hopefully with the aim of improving methods of communication across that interface, but you appear to simply want to impose some theoretical construct on a real situation that is nothing like as simple or as clean as you imagine. Just move on from the cliches! Really, how hard is that? – gavin]

“Friday, March 12, 2010
WUWT trumpets result supporting climate modelling
… This is expected from climate modeling. Nice to see someone else is picking up on this interesting confirmation of our scientific expectation. The prediction is old. In 1992 ….”

Gavin,
Strawman versus ideal types. Straw men are a trick used to win a debate. ideal types are something (social) scientists use to generalise vague and messy data (the social worlds is all but clean). Some social scientists, especially post-modern ones, prefer to describe the particulars in detail and not generalize. Both seems to evoke anger in the natural scientist. Perhaps the only language natural science accept, and understand, are numbers, quantification with statistical analysis, the language of the superior culture …

[Response: I don’t presume to speak for other scientists, but what annoys me is being generalized about without having any input into what the ‘boxes’ are. I’m a little surprised that it is ‘post-modern’ to be specific about an issue – I would have rather thought that this had always been a hallmark of useful analysis. We are far more likely to learn something useful about science/policy by looking at what happened during the acid rain or ozone depletion issues than by vague generalisations about what ‘scientists’ are or think. You are also (I think) mistaken in thinking that ‘scientists’ only respect numbers or statistics. This has nothing to do with a lack of respect for other academic disciplines, it is more a plea for greater engagement with your object of study. – gavin]

Care to make a substantial public bet under your real full name on the trend in sea ice over the next 3 decades? I’d be happy to take the “declining” side for total sea ice, both arctic and antarctic, if you want the “increasing” side.

Gavin,
Yes, annoyance are often a problem, especially in inter-cultural dialogue.

I agree with your ‘boxes’ argument. In addition to that it is important with a bit of history, to see where things are coming from. One is of course not post-modern on the merit of being specific about something.

Post-modernism is a reaction to modernism (a complex box). Modernism includes rationality, objectivity, the search for truth, laws of nature, progress, and many other things. Post-modernism is sceptical towards that. I tried to specificly adress one of these things, post-modern inspired research as a reaction to the scientific enterprice of generalising to find laws of nature and the like. But lets drop this sidetrack.

Yes, we can learn some things from acid rain or ozone depletion issues. For example, that these issues was contested by “sceptics” for the same reasons that climate change is contested by sceptics. We can also learn that uncertaintly was not critical to solve previous environmental problems. The DDT problem for example was solved despite great uncertaintly in the limited scientific literature. Why so? Because there was an easy technical solution to the problem. Climate change is different …

Perhaps Andreas Bjurström would like to link a short piece he wrote outlining his case about the “linear model”, the IPCC and related issues. I can’t figure out what his point is, though I tried. I think the low-probability risks are not dealt with seriously enough considering the weight they would likely have in a full risk assessment but that’s probably not his point.

I’m surprised he tries to blame anyone but social scientists themselves for their infatuation with numbers and (poorly understood) statistics. The humanities have largely resisted this trend and I don’t think they’re being disrepected as a result.

My impression of what Andreas Bjurström was trying to say was that it was valid, but not very well put. Here is an example of how relying on rational argument is not going to solve the problem of climate change.

It is an article from the magazine “Planet Earth” produced by the UK’s Natural Environment Research Council (NERC).

My point was something like: If reduced scientific uncertainty doesn´t make us more certain about what to do, than why is uncertainty so important? perhaps it is important primarily for participants of some scientific disciplines, e.g. it is their professional interest, not our interest. Moreover, the uncertainty regarding physical aspects are rather low (the issue all seems to be concerned with, including sceptics) whereas the uncertainty in biological systems and social systems is far greater. Why is the small uncertainty of the physical world so important when we successfully handle far greater uncertainties every day? (I get a feeling Im changing my point every time, but this was a try, and I honestly dont want to take up to much space here, but many people always reply to what I say here for some strange reason).

Try Roger Pielke Jr blog, he post something about the linear model etc. every other day.

101, Ric Merritt: Care to make a substantial public bet under your real full name on the trend in sea ice over the next 3 decades? I’d be happy to take the “declining” side for total sea ice, both arctic and antarctic, if you want the “increasing” side.

No. I claim no knowledge about future climate, other than that weather will fluctuate.

Of the bets available to me, I would rather bet that in 10 years time renewable alternative energy sources will be commercially competitive against petroleum without subsidies. I do not use enough electricity off the grid to justify purchasing a PV system, but I expect that within 10 years that will change; I review the math about 2 times per year to see if it is yet time to place the bet on a home PV system. If I were younger (I’m 63) I’d be investing in renewable energy companies.

I’d also discuss a bet about nuclear power, but nuclear has been declared off-topic.

Andreas, did you not read what I wrote? I said that the appropriate action is much more severe if, for example, CO2 sensitivitity is 4.5 or higher than it is if its between 2 and 3. The uncertainty makes it impossible at present to bound risk. Bounding risk is a prerequisite for policy and resource allocation for mitigation.

The bounds we are able to establish at present would demand we slam the brakes on fossil fuel consumption immediately.

The main point about uncertainty is that predictions by their nature are uncertain, and make many non scientists or less thoughtful people uneasy. When climate scientists express quite openly that the degree of future warming is uncertain, that is pounced on my the lazy or conflicted as an excuse to discard these predictions altogether. Many place more credibility in a preacher who tells them that they will go to heaven (or hell)- it’s the faux authority, not the content.

Dealing with predictive imprecision is second nature to scientists, but is the opposite for much of the public. This is an overlooked gap in communications between scientists and the public, and if it’s crossed a lot of things might become possible.

What we call here a Black Swan (and capitalize it) is an event with the following three attributes. First, it is an outlier, as it lies outside the realm of regular expectations, because nothing in the past can convincingly point to its possibility. Second, it carries an extreme impact. Third, in spite of its outlier status, human nature makes us concoct explanations for its occurrence after the fact, making it explainable and predictable. I stop and summarize the triplet: rarity, extreme impact, and retrospective (though not prospective) predictability.”http://en.wikipedia.org/wiki/Black_swan_theory

> … nothing in the past can convincingly point to its possibility.
> Second, it carries an extreme impact …

Harmen, the reason climate scientists study natural events in the past is to get a good idea what the many possible forcings are. Deep time is really astonishingly deep, and the paleo record is still accumulating.

But to worry about a ‘black swan attack’ event that has _ever_ occurred before, you need to imagine _two_ of them; one to subtract the forcing we now attribute to carbon dioxide based on known physics, and another to produce a comparable forcing out of some mysterious gray area unknown to science.

Have a look at the evolution ‘debates’ for the uses of the ‘gray area’ or ‘gaps’ argument to suggest some vast unknown force behind the curtain of time.

Often it’s just used to try to divert people from the known facts, e.g.:

“… when I meet a conservative AGW skeptic who says all that (and I have), I am all kisses and flowers. And so will be all the atmospheric scientists I know. That kind of statement is logical, patriotic and worthy of respect. It deserves eye-to-eye answers.

Harmen, what you are discussing is my continual reality in my day job. I am tasked to achieve multiple “nines” of reliability even while haveing test samples in the single (and sometimes low single) digits. Of course we cannot do this without having a model, and of course the model cannot be trained on completely representative data. It is the sort of problem that keeps a decent risk mitigation expert up at nights–all the more so when it involves the fate of human civilization.

I agree that past events cannot be guarantors of future behavior. However, we have a few billion years of Earth history to develop at least some sort of Bayesian Prior.

Denial for industries is a political-judicial-legislative-marketing tactic, not a philosophical position.

We may see much less funding for ‘advocacy science’ now that the Supreme Court has established a precedent, because providing denial as grist for advocacy (legal argument) is now not going to be needed at least in the US. Perhaps other countries and the EU will see more of it though.

Comment by t_p_hamilton — 1 July 2010 @ 10:29 PM
You were the one who mentioned pressure, not Mike or Gavin in his response to Mike.
—
RESPONSE: I know I was the one who brought up pressure and that was my whole point. Instead we got a simpler response from Gaving which did not inclued atmospheric pressure while mentioning Co2 and composition. What’s wrong with a simple obervation? Furthermore, could someone let me know how much of an effect, temperature wise, Venus’ very proximity to the Sun has on temperatures there>

Anyway, while on one of NASA’s websites I read something interesting about Venus.
Venus Express has certainly confirmed that the planet has lost a large quantity of water into space.
—–
“It happens because ultraviolet radiation from the Sun streams into Venus’s atmosphere and breaks up the water molecules into atoms: two hydrogens and one oxygen. These then escape to space.”http://www.astrobio.net/pressrelease/3536/was-venus-once-a-habitable-planet

(Please not that this quote is not intended to relate to AGW – just something I found interesting – snip at will!)

I am certainly not trying to distract from the facts.I subscribe to the conclusions of the IPCC reports but if we only focus on the facts then i think we will do to little about rising GHG concentrations.

The IPCC tends to focus on effects are likely or very likely. That is good from a scientific perspective..

But when we talk optimal policy (optimal carbon cap)and decision making under uncertainty i think we also have to make risk assesments..

i.e. we also have to think about low probability consequences of carbon emissions that could have an extreme impact.

Let me try to explain by an example…

Consider the possibility there is a link between temperature and earthquakes/tsunamis..

Global warming may bring tsunami and quakes: scientists
By Richard Meares
LONDON | Wed Sep 16, 2009 5:07pm EDT
……….
Speakers were careful to point out that many findings still amounted only to hypotheses, but said evidence appeared to be mounting that the world could be in for shocks on a vast scale.
………..http://www.reuters.com/article/idUSTRE58F62I20090916

OK, I checked Pielke Jr.’s blog and found an entry on the “linear model”. It’s science -> public opinion -> policy. Some commenters here seem to think according to something like this model. But this is clearly not what the IPCC is about (the I stands for intergovernmental!). Who actually works according to this model? I guess this is what Hansen might be doing (some of the time anyway). Who else?

Andreas, the way you use of general pronouns like “we” makes it impossible for me to understand what you’re trying to say. If you’re a social scientist, then you must know how to describe what goes on in societies more effectively.
Yes, there are uncertainties which mainly concern the scientists. But there are physical uncertainties with a broader relevance. Best not generalize so much if you don’t have anything to say which would apply to all uncertainties. Surely you’re not suggesting that, say, ice sheet dynamics are irrelevant to the huge public works which would protect low-lying areas against flooding.

Hank (115), I was quite impressed with your referenced Brin’s commentary on skeptics vs deniers. He went off the track a couple of times IMO by doing some of the negative things he was describing like that old chestnut of the tobacco-climate cabal, and the petro-media conspiracy. But I would give him some leeway. I thought it very astute and insightful.

Harmen,
While I agree that we should be cannot ignore low-probability, high-consequence events, we already have the problem that risk cannot be bounded even if we confine ourselves to increased drought, flooding due to impulsive rain events and the impact of variable climate on agriculture. This leaves us comparing a series of unbounded risks–hardly ideal from a mitigation perspective.

If this were a satellite project, the appropriate approach would be to slam on the breaks and try to refine the risks less conservatively while working out mitigations. Or put another way, risk avoidance is the only viable mitigation approach under such circumstances.

Jimbo, I’m probably not the best person to answer your question, but until the big guns deem it necessary to respond I’l through out a few tidbits:

Of course the greater insolation at Venus’ distance from the sun does matter. It is interesting however that the total absorbed solar radiation per meter squared on Venus is less than on the earth. This is a consequence of the high albedo from the dense cloud cover. To risk being off by a few hundredths earths albedo is roughly 30%, and Venus’ is roughly 70%. So total solar absorbed radiation is actually less on Venus. But, I’m pretty certain that the higher solar constant drove the processes which created the runaway greenhouse effect. But once you get that strong a greenhouse effect, higher cloudbased albedo just doesn’t help enough.

The loss of water is interesting. It requires enough water of hydrogen to get high into the planets exosphere, so that the low molecular weight/ high velocity hydrogen can escape. The fact that Venus’ magnetic field provides little protection from the solar wind, (I think) also increases the loss mechanism. It should be noted that young solar type stars, because of their likely much faster spin rates have very much stronger solar winds (perhaps a hundred times).

Does anyone have a link for any interesting speculative natural histories of Venus?
i.e. presumably the slow rotation and the approx zero magnetic field are linked? If Venus always rotated this slowly would water not have boiled on it’s day side in a pre-high-albedo pre-super-greenhouse point in history?

Would any decent atmospheric water content combined with no magnetic field lead to the vast bulk of its hydrogen being lost to space and the supergreenhouse arising due to no hydrological cycle (rather than some runaway point when previously stable oceans reached boiling point)?

What mechanisms could have caused some putative early Venus with a “more normal” rotation period and a magnetic field (and potentially a biosphere) to change into the present very slow rotation no magnetic field state? If the only answer is massive asteriods etc could any biosphere have survived the magnitude of the impact required to make the change anyway?

The Uncertainty Prayer should be posted prominently on the walls of all policy analysts/decision-makers.

Few people posting in this thread actually are speaking to the content of the referenced white paper. I found it interesting reading.

Not being an expert on GCMs, I would be very interested to read the comments of any of the resident gurus (Gavin?) on any of the points in the paper.

Especially:
3.1.8 How well do the models reproduce past climate, variability, and extremes?

The paper also offers options for investments in modeling and data gathering to reduce uncertainty for regional forecasts, but with a range in climate sensitivity of 2 – 4.5 C/ doubling of CO2e, and uncertainty in levels of future emissions, it becomes apparent that the best that can be hoped for is a substantial range…which brings us back to the Uncertainty Prayer.

And a related prayer that decision-makers see the need for reducing emissions to near-zero ASAP, and find the wisdom to make it happen.

Other people do quite reasonably claim *some* knowledge about future climate. The usual uncertainties cited do not cancel all knowledge, or if you prefer, predictive power. Your retreat to know-nothingness is a miserable cop-out made inevitable by starting from an untenable position. (Hint: to those of us with time served in academia, “untenable” is way worse than “wrong”.)

AIC (#134),
I’m obviously no guru but check the “index” link at the top of the RealClimate home page. The stuff under the heading “sensitivity” is relevant to your query, especially the “plus ca change” entry. I also recommend the “target CO2″ and “methane hydrates” entries for additional uncertainties not taken into account in your quote.

There is a heat wave in the eastern US, and everyone is aghast. But the temp anomaly map indicates there is no anomaly there. Is everyone just forgetting that it gets hot on the east coast in the summer, or is the anomaly map wrong?